The United States last week called for Russia to probe reported election fraud as the West warily marked Vladimir Putin's return to the Kremlin amid congratulations from Asia and the Balkans.

Washington hoped Moscow would carry out an "independent, credible" investigation, said US State Department spokeswoman Victoria Nuland, after foreign monitors found the results had been skewed in Putin's favor.

Putin secured almost 64 percent of the vote in the election, winning back the Russian presidency he held for two terms from 2000-2008 before he took a four-year stint as prime minister.

But international observers led by the Organization for Security and Cooperation in Europe OSCE) said while there had been progress in transparency, the campaign had been massively tilted in favor of Putin.

"Conditions (for the campaign) were clearly skewed in favor of... Vladimir Putin" while the vote count was "assessed negatively in almost one-third of polling stations observed due to procedural irregularities," they said.

Hundreds protested Putin's comeback on the streets of Moscow after the election, some shouting out "disgrace," with police moving in to disperse the demonstrations and arresting dozens.

Nuland said Washington endorses the preliminary report by the OSCE and the Parliamentary Assembly of the Council of Europe (PACE).

And she added, without mentioning Putin by name, that the United States "looks forward to working with the president-elect after the results are certified and he is sworn in."